Ear Embryology

Question 1

When and where do eyes first become evident in the developint embryo?

Answer 1

as optic (lens) placodes on the sides of the head around 4.5 weeks

Question 2

When is the most critical period for eye development?

Answer 2

4-8 weeks (but really development continues after birth

Question 3

What embryonic layers contribute to the eye?

Answer 3

neuroectoderm and surface ectoderm

Question 4

What part of the developing brian does the eye stem off of?

Answer 4

diencephalon

Question 5

What is the first step in eye development?

Answer 5

Before the rostral neuropore closes, you get formatin of optic grooves (eary in week 4)

Question 6

What will the optic groove do?

Answer 6

It will evaginate outward so that the neural epithelium pushes outward through the mesenchyme towards surface ectoderm

This forms the optic vesicle.

Question 7

What structure connects the optic vesicle to the rest of the idencephalon?

Answer 7

the optic stalk

Question 8

During week 5, the optic vessicle folds back on itself to form what?

Answer 8

the optic cup

Question 9

What are the layers of the optuc cup?

Answer 9

It’s a double walled structure with an outer and inner layer separated by the itnraretinal space

the inner layer will become neural retinal and the outer layer will become RPE

Question 10

What induces the formation of the lens placode?

Answer 10

the optic cup

Question 11

What does the lens placode do?

Answer 11

It invaginates and pinches off to sink down below the surface ectoderm. This is the lens vesicle and will eventually become the definiitive lens

Question 12

During development, what artery supplies the lens vessicle?

Answer 12

the hyaloid artery

Question 13

The creases of the optic cup approximate and fuse, tucking a fold of the neural tissue into the optic stalk. What is the inward creese called?

Answer 13

the choroid fissure (or optic fissure)

Question 14

What usually happens to the hyaloid artery?

Answer 14

It persists until around 11 weeks, at which point it starts regressing - usually complete by about 8 months, but sometimes can persist into adulthood

Question 15

THe hyaline artery becomes enclosed in the choroid fissure when the ends fuse together. What will this artery become then?

Answer 15

the central artery of the retina (the central vein joins it too, but i”m lazy)

Question 16

What happens with a congenital coloboma?

Answer 16

you have defective closure of the choroid fisure, resulting in a key-hole deformity of the pupil.

Question 17

An anterir coloboma is most common, but what symptoms will occur with a posterior coloboma?

Answer 17

the retina can be involved and there won’t be any neural ectoderm in the area where it didn’t fuse

this means you’‘ll have a huge blindsport

Question 18

What does the retina form from>

Answer 18

the two layers of the optic cup

Question 19

What induces the formation of the neural retina, choroid, and sclera?

Answer 19

the RPE

Question 20

What is the ora serrata?

Answer 20

the junction between the multilayered photosensitive and simple non-photosensitive region of the retina

Question 21

What will cuase re-establishment of the intraretinal space?

Answer 21

a detached retina - usually as a result of trauma

Question 22

In what layer of the iris do the sphincter and dilator pupillae muscles develop? Why are they special developmentally?

Answer 22

They develop in the neuroectoderm layers of the iris

it’s an exception to the general rule that muscles develop from mesoderm

Question 23

What is the pupillary membrane? What does its surround?

Answer 23

It’s remnants of mesenhyme on the anterior surface of the lens - usually disappears, but sometimes pieces can persista nd cause vision problems

Question 24

What does the mesenchyme between the lens and the retina differentiate into?

Answer 24

vitreous body wiht virteous humor

Question 25

What forms the choroid and sclera?

Answer 25

they’re layers that form from the surrounding mesenchyme, induced by the RPE

Question 26

What layer is the equivalent of the arachnoid and pia around the optic nerve? Which is equivalent with the dura?

Answer 26

arachnoid and pia = choroid

dura = sclera

Question 27

What induces the surface ectoderm to form the epithelium of the cornea and conjunctiva?

Answer 27

the lens

Question 28

What are the 3 layers of the cornea?

Answer 28

epithelium (from surface ectoderm)

stroma (from mesenchyme)

endothelium (from neural crest cells)

Question 29

At what week in development do the eyelids fuse? When do they reopen?

Answer 29

fuse around 10 weeks

open around 26 weeks

Question 30

What is the classic triad of rubella associated congenital defects?

Answer 30

congenital cataracts

deafness

cardiac effects

Question 31

What muscle needs to be tightened to fix congenital ptosis?

Answer 31

levator palpebrae

Question 32

What is anopththalmia and microphthalmia and what is the treatment?

Answer 32

anophthalmia - no eye

microphthalmia - small eye

you put spacers into the orbit to gradually widen, and then use prosthetics